Polyploidy, Hybridization, and the Invasion of New Habitats

Post-glacial evolution of Panicum virgatum: centers of diversity and gene pools revealed by SSR markers and cpDNA sequences

“…Early studies of polyploidy demonstrated that simple hypotheses, such as greater tolerance to environmental stresses, cannot explain adaptive differentiation between ploidy levels (Stebbins 1985) and our studies of switchgrass support this conclusion (Casler et al 2004(Casler et al , 2007b. Rather, Stebbins (1985) hypothesized that higher polyploids are more capable of invading and colonizing new or disturbed habitats.…”

“…Early studies of polyploidy demonstrated that simple hypotheses, such as greater tolerance to environmental stresses, cannot explain adaptive differentiation between ploidy levels (Stebbins 1985) and our studies of switchgrass support this conclusion (Casler et al 2004(Casler et al , 2007b. Rather, Stebbins (1985) hypothesized that higher polyploids are more capable of invading and colonizing new or disturbed habitats. Duplicate genomes present in allopolyploids would provide one level of benefit, while polysomic inheritance within each genome would create a second benefit: cryptic genetic variability to enhance the ability of populations to respond to fluctuating environments and to produce progeny capable of colonizing new environments.…”

“…Polyploidy is the rule in switchgrass and higher ploidy levels, such as 8x, are very common, particularly at higher latitudes. Polyploids are capable of storing huge amounts of cryptic genetic variability that would be useful under fluctuating environmental conditions, allowing populations to use natural selection as a long-term survival mechanism (Stebbins 1985;Symonds et al 2010). The nearly obligate allogamous mating strategy of switchgrass encourages cross-pollination among diverse individuals and helps to preserve genetic diversity through a highly heterozygous genome (Martinez-Reyna and Vogel 2002;Vogel 2004).…”

“…Duplicate genomes present in allopolyploids would provide one level of benefit, while polysomic inheritance within each genome would create a second benefit: cryptic genetic variability to enhance the ability of populations to respond to fluctuating environments and to produce progeny capable of colonizing new environments. Because the success of invaders or colonists depends on the creation of favorable gene combinations, the allopolyploid and autopolyploid nature of octoploid switchgrass (Vogel 2004) may explain the significantly higher frequency of octoploid genotypes in habitats colonized during post-glacial migrations (Stebbins 1985). Indeed, if octoploid genotypes have a higher probability of colonization success, cyclic ice ages would have repeatedly created conditions under which these genotypes were favored over tetraploids, creating a persistent driver for regeneration and reestablishment of octoploid populations at more northern latitudes.…”

Dated historical biogeography of the temperate Loliinae (Poaceae, Pooideae) grasses in the northern and southern hemispheres

“…The origin of most of the Loliinae lineages and of other temperate grasses has been usually associated with the recent geological and climatic changes of the late Tertiary and the Quaternary periods (Stebbins, 1985;Charmet et al, 1997;Balfourier et al, 2000;Fjellheim et al, 2006). Previous molecular-clock estimates deduced from the divergence between rice and wheat indicate a late Miocene (9 My) origin of the broad-leaved and fine-leaved Festuca lineages (Charmet et al, 1997), supporting these recent historical scenarios.…”